Ultra short wave system



Get. 15, 1940. USSELMAN ET AL 2,218,223

ULTRA. SHORT WAVE SYSTEM Filed June 24, 1937 ANTENNA INVENTORS .6. L. USSEL MAN AND c. H 5511.

AiTOfiNEY 8/45 RECTIFIER MM on. is, 1940 orr ce ULTRA SHORT CAVEv SYSTEM George I... Usselman and; Clarence W.. Hansel]; Port Jefferson, N.v Y., assignorsto Radio Gov poration. of- America, a corporation of Dela ware Application June'24, H37, SeriaI'No. 150,024 7 26 Claims.

This invention relates to short wave communication systems.

One of. the objects. of the present. invention is to provide a sharply tuned oscillation, generator system which delivers approximately constant energy to a load throughout a range of frequencies.

Another object is to provide an electron discharge. device oscillation generator system con- 10 trolled as to frequency by a tuned, low loss, con.-

centric resonant line, wherein the anode of the electron discharge device is grounded for radio frequency energy.

A feature of the invention lies in the manner 1'5" of coupling the grid and cathode of a groundedanode electron discharge device oscillator to the inner conductor of a concentric resonant frequency controlling line.

Another feature resides in the use of a con.-

- ducting loop connected across a transmission. line, in combination with a pair of condensers for controlling the impedance of the load circuit. overa range of frequencies. The loop is designed to have an overall lengthequalto. half'the length of the shortest wave of the range.

A further feature lies in the use of: a dished or bowed end plate: of the resonant line used for connecting the inner and outer conductorsto:- gether. The design of this end plateprevents warping or buckling by heat engendered. therein during the operation of the system, with a. consequent change in resonant frequency of the line.

A still further feature is the frequency sweep arrangement used for periodically varying the resonant frequency of the line. This particular frequency sweep employs a cam and geared motor for varying the efiective length of the inner conductor.

Other objects and features, and their advan; V tages, will appear in the following description which is accompanied by a drawing, in. which the single figure illustrates, partly schematically and partly in section, a high frequency transmission system embodying the principles of theing an. electrondischarge'device I whose fre-- quency is controlled by a concentric resonant line having an outer grounded conductor 2 and an inner conductor 3. Inductively coupled tothe inner conductor are the grid. and filament leads" 20 and 2|, 2|, respectively, of the electron; discharge device, and also a transmission line TL terminating in an antenna, asshown. The anode of electron discharge device I is connected to ground for radio frequency, energy through bypasscondenser 4-. Similarly, the remote ends of: the grid and filament leads are also connected to. ground for radio frequency energy through by- 5 pass condensers 5, 5. By-pass: condensers l and 5;. 5 are designedto have, connections of practically zero iength,inorder to be: effective at the ultra high frequencies used in. the system.

A full wave. rectifier IOis: employed to provide: 10 a positive polarizingpotential'to the anode of the electron discharge device I, while a source of alternating current. energy supplies fllainentheat ing energy over leads. II and. transformer I2. Resistors I3' and ll 'function as fllament'andgrid'. 1'5 biasing resistors, respectively. Resistor I32 in the filament ground-.circuittservesto maintain a-positive biasfpotential'. on the filament on device I when: anode current. flows, thus: protecting the electron discharge device if oscillations cease. 20 Resistor I4 is a. grid. "lealr resistor of the order of? 6.000 ohms; which supplies; negative bias to the grid of device I: when. grid current flows.

The concentric line; for controlling. the fre-- quency of electron discharge. device. I comprises 25 an. inner conductor 3 and; an outer conductor 2 which are directly connected. together at one of their adjacent ends by means of a dished or bowed end: plate 32. A. flexible metal bellows 6. at

theopenend' of the inner conductor, and an Invar 3 rod. I within the inner conductor 3', help to maintain constancy of frequency with change intemper-ature. Since the length of the projection of the inner conductor 3'upon the outer-conductor 2 determines, generally, the resonant frequency ofi35 the concentric line, it will be appreciated that adjustment of the bellows Ii through rod I will change the effective length: of the inner conductor and the frequency of the line. The frequency of w the transmitter may thus be adjustedto anyde v sired point in. the transmitter frequency range obtained-by moving. rod. 'I-iin'or out by a handle. (not shown) in order to shorten: or lengthenthe metal bellows 6,. which, in effect, shortens or" lengthens. the-inner conductor 3. Reference is 45 i surface being the other condenser plate.

ductors 2 and I are closely coupled together, that is, at the shorted end of the line where the end plate 32 is located. Since the center of the end plate 32 is hottest, there is a tendencyfor it to warp or buckle in or out, thus tending to change the position of the inner conductor 3 to some unpredictable position with a consequent change in the resonant frequency of the line. In order to prevent such a sudden unpredictable change in frequency, due to buckling, snapping, or warping of the end plate by heat, the end plate 32 is dished or bowed either in or out, asshown. The position of conductor '3 is thus predictable and may be compensated for in the adjustment of rod I.

If a continuous change of frequency of the transmitted oscillations over a band is desired, there is provided a' frequency sweep arrangement consisting of a cam 83a suitable gear 22 linked to the cam by a shaft 25, anda motor 23 for varying periodically the frequency of oscillations. Cam 8 is arranged to engage rod 1 for continuously changing the length of the bellows 6. Motor 23 may be stopped through switching means 24, to prevent periodic frequency variation from taking place. This method of obtaining. a frequency sweep will be referred to later in connection with the arrangement used for keying the system.

A fan 9 at one end of the resonant line is used to blow air through the line for cooling purposes;

In one embodiment actually tried out in practice, for generating oscillations of a frequency of the order of 90 megacycles, the oscillator electron discharge device I was located within the resonant line and consisted of an evacuated device whose anode was conductively coupled to a massive hub located externally of the envelope of the device and having numerous: cooling fins. The

, fan 9 caused a stream of air to pass. not only through the resonant line but also past the fins of thel-air cooled tube anode to keep the anode cool and prevent excessive heating which might be detrimental to the efficient operation of the transmitter. For a more detailed description of such a device having cooling fins for the anode,

reference is made to a copending Patent No. 2,176,657, granted October 1'7, 1939, to J. L. Finch. In the above mentioned embodiment of the invention, the connections to the by-pass condensers 4 and 5, 5 were made of minimum length and substantially zero inductance by using the groundsurface (i. e., the outer surface of conductor 2 of the resonant line) as one condenser plate of each by-pass condenser. Condensers 5, 5 were actually made of special construction by widening out the filament and grid conductors 20 and 2|, respectively, in the form of plates and insulating them with mica dielectric, the ground As for condenser 4, the clamp holding the air cooling fins of device 1 formed one condenser plate while the ground surface of line 2 formed the other condenser plate. A Bakelite sheet comprised a direct current insulator and radio frequency dielectric for condenser 4.

Transmission line TL is shown coupled to the inner conductor 3 by way of serially connected condensers I5, l5 and loop it, one of whose points I! (approximately the center point) is grounded by a connection is which is adjustable in posi tion over H; for a reason described later.

In order to derive substantially constant output energy from the oscillation generator over a electron discharge device I is arranged to have greater coupling to conductor 3 by the arrangement of grid lead 20 than the filament has through filament leads 2|. In other words, the grid must be excited periodically at higher radio frequency potentials than, but in phase with, the filament for best oscillating conditions. Putting it still another way, the grid is driven harder than the filament.

Inasmuch as in this type of oscillator (in which the anode is grounded for radio frequencies) it is inconvenient to change the coupling of the device I to the resonant line or the regeneration of the device I, as the frequency-is varied by changing the effective length of the line, the amplitude of the generated oscillations will not.be constant over a wide range of certain of the high frequencies, and the tendency will be for less power output at the higher frequencies and more power output at the lower frequencies in the range. This is believed to be due to the fact that there is an optimum value of coupling between vacuum tube and resonant line for a particular length of inner conductor, and as the length of this inner conductor is changed in order to change the frequency of the oscillations the coupling will also change and the voltage and current in the resonant line will fall off with change in the length of the line from the optimum value. In practice, the change in power output is not serious until certain limiting lengths for the resonant line are reached. This tendency for change in power output is overcome in the present invention by the provision of the transmission line circuit including the coil l6, condensers I5, I 5 and wire loop l9. By shifting the grounding lead I8 to the proper point on coll I6, there will be obtained I balanced output on the two conductors of transmission line TL. Condensers l5, ii are adjusted to have a suitable value (determined experimentally) so that at the higher frequencies of the range the condensers will have maximum bypassing effect. Since loop of wire I9 is a half wavelength long, overall length, but one-quarter than at the higher frequencies; consequently the lower frequency energy will pass through the con- I 2,218,228 .and the energy delivered to the load (antenna) is between 81 and 86 million cycles. These frequencies are merely mentioned by way of illustration, and are not to be construed as limitative of the invention.

One advantage of this invention is that there is required no separate polarizing battery for the grid, except when keying is employed, since both the grid and filament obtain their proper excitation by the arrangement of the respective leads near the inner conductor 3.

In the design of the system of the invention it is very desirable to avoid resonance effects in the coupling loops 20, 2| at or near the operating frequencies, because such resonance effects will produce parasitic oscillations and certain changes in the value of coupling between the loops and the resonant line.

If it is desired to key the transmitter of the invention, i. e., transmit telegraph signals in accordance with the movement of a key, there may be provided in the manner shown in the drawing, a resistance 33 of the order of 100,000 ohms, a bias rectifier 26', a one microfarad condenser 21, a low resistance 28 of the order of 75 ohms, a switch 30, another resistor 3| of the order of 10,000 ohms, and a key 29. With such an arrangement, keying of the transmitter oscillations is effected as follows: As soon as the frequency reaches the desired point for keying, switch 24 'is opened and switch 30 moved to engage its right hand terminal. Closure of switch 30 to the right will effectively insert 100,000 ohm resistor 33 in the circuit in series with the grid leak resistor l4, and at the same time connect the negative terminal of the bias rectifier 26 through the '10,000 ohm resistor 3| to the grid circuit; Condenser 21 and resistor 28 are connected in series across the contacts of key 29 to prevent destructive arcing between the key contacts during keying. The transmitter is now ready to be keyed. When the key 29 is up, current from .the bias source 26 flows from the 10,000 ohm resistor 3| through the 100,000 ohm resistor "33 in the grid circuit, thereby causing a high negative voltage to appear on the grid of electron discharge device I so that no oscillations can start, since the .vacuum tube is biased past cut-off. If the key 29 be pressed down, the 100,000 ohm resistor 33 in the grid circuit is short circuited and also the bias source 26 is shorted throughthe 10.000 ohm resistor 3| (resistor 3| is used to prevent completely short circuiting and damaging the bias rectifier 26). At this instant the device I has no bias on its grid. Consequently anode current will flow and oscillations build up. The grid is thereby excited and the flow of rectified grid current through the 6,000 ohm resistor l4 furnishes normal operating bias during the time of oscillation. Now, if the key 29 is lifted, the 100,000 ohm resistor 33 is inserted again in the circuit and the fiow of grid current to ground (to the cathode) is greatly reduced by this high resistance, consequently the excess grid currentfiows into and charges the 1 mi. condenser 21 until it reaches a potential equal to the peak grid voltage (due to excitation). When this amount of grid bias voltage is reached, the transmitter will stop oscillating when the first dip in excitation energyoccurs which, for practical purposes, is almost instantly. Now, assuming that there is no fixed bias source 26, then as the charge leaks out of the 1 mf. condenser 21 through the 100,000 ohm resistor 33, the grid bias will be reduced to the point where oscillations again start only to be stopped by the charging of the 1 mi. condenser 21 due to the increased bias. This process would continue indefinitely as long as the key is up, sending out pulses of oscillations. In order to prevent this start and stop of oscillations withkey up, we

supply a fixed negative bias potential from source 26 through a resistor 3| (about 10,000 ohms in this case). The voltage value 'of this fixed bias need only be sufiicient to maintain cut-off of the electron discharge device anode current, although a somewhat higher value of fixed bias is desirable.

When it is desired to use the frequency sweep arrangement employing cam 8 and motor 23, the keying is stopped and continuous oscillations are permitted by moving the switch 30 to the left. The sweep motor is started by closing switch 24. Closing switch 30 to the left disconnects the fixed bias source 26 from the grid circuit and short circuits the 100,000 ohm resistor 33 in the grid circuit to allow normal operating biasto exist,

on the grid during the time of oscillations.

It is to be understood that the term ground" used in the specification and appended claims means any point or surface of zero or fixed radio frequency potential. What is claimed is:

1. In a high frequency system, an oscillation generator for producing oscillations whose amplitude is approximately proportional to decrease in frequency, means for controlling the frequency of said oscillations and for varying the same over a desired frequency range, a transmission medium coupled to said oscillation generator whose impedance increases approximately proportionately to the decrease in frequency, and to such an extent as to compensate substantially entirely for the ,variation in amplitude of said generator and a load coupled to said transmission medium.

2. In a high frequency system, an electron discharge device oscillation generator for producing a range of oscillations whose amplitude increases-and decreases with decrease and increase, respectively, in the frequency of oscilla tions generated, a utilization circuit, a transmission medium coupled between said generator andv utilization circuit, said medium having the characteristic of increasing and decreasing impedance with decrease and increase, respectively, of the frequency, whereby a substantially constant output is delivered to said utilization circuit over said range, and means for periodically varying a utilization circuit, and a transmission medium coupled between said generator and utilization circuit, saidmedium comprising a two conductor line. a condenser in series with each conductor of said line of a suitable value to pass the higher frequencies of said range with minimum attenuation, and a U-shaped loop of wire in shunt with 'said line, the legs of said loop having a length approximately equal to one-quarter wavelength at the highest frequency of said range, whereby energy of substantially constant value is passed to said utilization circuit.

4. A system in accordance with claim 3, characterized in this that said utilization circuit is an antenna, and said loop is coupled across said twoconductor line on the side of the condensers nearest said antenna.

transmission mediumcoupled between said generator and utilization circuit, said medium having the characteristic of increasing and decreasing impedance with decrease and increase, respectively, of the frequency, whereby a substantially constant output is deliveredto said utilization circuit over a range of frequencies.

6: In a high frequency system, an electron discharge device oscillationgenerator for producing oscillations over a range of frequencies, said device having an anode, a cathode and a grid, a capacitive connection from said anode to ground for by-passing radio frequency energy from said anode, means for exciting said grid at a higher potential than and in phase with said cathode, whereby oscillations are produced whose amplitude increases approximately proportional to the decrease in frequency, a utilization circuit,

and a transmission medium coupled between said generator and utilization c'ircuit, said medium comprising a two-conductor line, a bypass condenser in series with each conductor of said line of a suitable valueto pass the higher frequencies of said range with minimum attenuation, and a loop of wire in shunt to said line, the length of said loop being approximately onequarter of a wavelength at the highest frequency of said range, whereby energy of substantially constant value is passed to' said utilization cirwit.

7. In a high frequency system, an electron discharge device oscillation generator for producing oscillations over a range of frequencies,

said device having an anode, a cathode and a grid, a capacitive connection from said anode to ground for by-passing radio frequency energy, and a frequency control circuit for said generator comprising a concentric resonant line having inner and outer conductors suitably coupled together, loops of wire extending from said grid and cathode, respectively, within said resonant line for inductively coupling to the inner conductor of said line, said loops of wire being so arranged that said grid loop is excited at a higher potential than said cathodeloops.

8. In a high frequency system, an electron discharge device oscillation generator for producing oscillations over a range of frequencies, said device having an anode, a cathode and a grid,

a capacitive connection from said anode to ground for by-passing radio frequency energy, a

frequency control circuit for said generator comprising a concentric resonant line having inner and outer conductors suitably coupled together,

loops of wire extending from said grid and cathode, respectively, within said resonant line for inductively coupling to the inner conductor of said line, said loops of wire being so arranged that said grid loop is excited at a higher potential than said cathode loops, whereby the amplirange, whereby energy of substantially constant value is passed to said utilization circuit.

9. In a high frequency system, an electron discharge device oscillation generator for producing oscillations over a range of frequencies, said device having an anode, a cathode and a grid, a capacitive connection from said anode to ground for by-passing radio frequency energy. and a frequency control circuit for said generator comprising a concentric resonant line having inner and outer conductors coupled together more closely at one of their adjacent ends than at their other, means for exciting said grid in phase with but at higher radio frequency potentials than said cathode, said means comprising loops of wire located within said resonant line extending-from said grid and cathode, respectively, to ground for inductively coupling said electrodes to said resonant line, a bias resistor for said cathode electrode for maintaining said cathode at a positive potential with respect to ground when oscillations cease, and a bias resistor for said grid for maintaining said grid at a negative potential with respect to the cathode when the grid current flows.

10. In a high frequency system, an electron discharge device oscillation generator for producing oscillations over a range of frequencies, said device having an anode, a cathode and a grid, a capacitive connection from said anode. to ground for by-passing radio frequency energy,

and a frequency control circuit for said generator comprising a concentric resonant line having inner and outer conductors suitably coupled together, loops of wire extending from said grid and cathode, respectively, within said resonant line for inductively coupling to the inner conductor of said line, said loops of wire being so arranged that said grid loop is excited at a higher potential than said cathode loops, a negative bias potential source, and means for switching in a high resistance and for connecting in said negative bias potential source to the grid circuit of said electron discharge device, there being keying means connected across said high resistance when it is desired to prepare said system for keying.

11. In a high frequency system, an electron discharge device oscillation generator for producing oscillations over a range of frequencies, said device having an anode, a cathode and a grid, a capacitive connection from said anode to ground for by-passing radio frequency energy, and a frequency control circuit'for said generator comprising a. concentric resonant line having inner and outer conductors coupled together more closely at one of their adjacent ends than at their other, loops of wire extending from said grid and filament, respectively, within said resonant line for inductively coupling to the inner conductor of said line, said loops of wire being so arranged that said grid loop is excited at a higher potential than said filament loops, and keying means for producing a high negative bias on said grid to cause oscillations to cease, in accordance with the signals to be transmitted.

12. In combination, an electron discharge device oscillation generator having coupled thereto a frequency controlling circuit comprising a tuned circuit in the form of a concentric line having an inner conductor and an outer conductor, means for coupling said conductors'together at one end, and means for varying the frequency of oscillations produced over a predetermined band by continuously varying the effective length of said inner conductor.

13. In a high frequency system, an electron discharge device oscillation generator for producing oscillations whose amplitude changes with change in frequency, a utilization circuit, and a transmission medium coupled between said generator and utilization circuit, said medium having the characteristic of changing its impedance to the flow of energy ther'eover as the frequency of the oscillations produced. by said generator changes, whereby a substantially constant output is delivered to said utilization circuit, and means for periodically varying the frequency of said oscillations.

14. In a high frequency system, an electron discharge device oscillation generator for producing oscillations whose amplitude changes with change in frequency, a utilization circuit, a transmission medium coupled between said generator and utilization circuit, and a network coupled to said medium for maintaining the impedance thereof to the energy produced by said generator substantially constant, whereby substantially constant power output is delivered to said utilization circuit, and means for periodically varying the frequency of said oscillations.

15. In a high frequency system, an electron discharge device oscillation generator having coupled thereto a frequency controlling circuit comprising a tuned circuit in the form of a concentric line having an inner conductor and an outer conductor, means for coupling said conductors together at one end, a metallic bellows attached to said other end of said inner conductor, a rod located within said inner conductor, said rod being fastened at one. end to said bellows and having its other end extending externally of said concentric line, and means linked to said rod for continuously lengthening and shortening said bellows for varying the effective length of said inner conductor for varying the frequency of 0scillations produced over a predetermined band.

16. A system in accordance with claim 15, characterized in this that said last means comprises a cam and a motor for driving said cam at a predetermined speed.

17. In a transmitter, the combination with an oscillation generator Whose output voltage in-.

creases and decreases with decrease and increase of frequency, respectively, of a load connected to said I generator through a path whose impedance'increases and'decreases as the frequency decreases and increases respectively, whereby the energy delivered to said load is approximately constant over a range of frequencies.

18. In a high frequency system, thecombination with an oscillation generator whose output voltagevaries with frequency, meansforperiodically varying the frequency of saidigenerator. over a range of frequenciesaof a load connected to said generator through a, path whose impedance varies with frequency in such sense and to such an extent as to compensate substantially entirely for the variation in output voltage, whereby approximately constant energy is delivered to said load. 7 r

19. In a high frequency system, an electrorn discharge device oscillation generator for producing oscillations, said device having an anode, a cathode and a grid, a capacitive connection frequency energy, and a frequency control circuit for said generator comprising a concentric resonant line having inner andouter conductors suitably coupled together, and meansfor coupling said grid and cathode to said resonant line such that said grid is excited at a higher potential than, but in phase with, said cathode.

, 20. In a high frequency system, an electron discharge device oscillation generator for producing a range of oscillations whose amplitude increases and decreases with decrease and increase, respectively, in the frequency of oscillations generated, a utilization circuit, a transmission medium coupled between said generator and utilization circuit, said medium having the characteristic of increasing and decreasing impedance with decrease and increase, respectively, of the frequency, whereby a substantially constant output is delivered to said utilization circuit over said range, a frequency stabilizing element for said oscillation generator, and means acting on said stabilizing element for changing the frequency of the produced oscillations.

21. In a high frequency system, an electron disvoltage varies with frequency, of a load connected to said generator through a two-wire transmission line, and a U-shaped loop having a length approximately equal to one-quarter wavelength at the highest operating frequency of said generator connected at its open ends across said line, whereby approximately constant energy is delivered to said load.

23. In a, high frequency system, an electron discharge device oscillation generator for producing oscillations over a range of frequencies, said device having an anode, a cathode and a grid, a capacitive connection from said anode to ground for by-passing radio frequency energy, and a frequency control circuit for said generator comprising a concentric resonant line having inner and outer conductors suitably coupled together, and means for inductively coupling said grid and cathode to said resonant line such that said grid is excited at a higher potential than, but in phase with said cathode.

24. In a transmitter, the combination with an oscillation generator whose outputvoltage varies with frequency, of a load connected to said generator through a path whose impedance varies with frequency in such sense and to such an extent as to compensate for the variation in output. voltage, whereby approximately constant energy is delivered to said load, said path comprising a two-conductor transmission line having a condenser in each conductor of said line.

25. In a high frequency system, an electron discharge device oscillation generator for producing oscillations over a range of frequencies} said device having an anode, a cathode and a grid,

a capactive connection from said anode to ground for by-passing radio frequency energy, and a frequency control circuit for said generator comprising a concentric resonant line having inner and outer conductors suitably coupled together,

and means for coupling said grid and cathode to said resonant line such that said grid is excited at a higher potential than, but in phase with said cathode, and means for changing the resonant frequency of said line.

26. In a radio transmission system, an oscillation generator whose output voltage varies with frequency, means for periodically varying the frequency of said generator over a range of frequencies, an antenna, and connections from said oscillation generator to said antenna including a network whose transmission characteristics are so chosen as to compensate substantially entirely for the variation in output voltage, whereby approximately constant energy is delivered to said antenna.

' GEORGE L. USSELMAN.

@ CLARENCE W. I-LANSEIL. 

